wordpress使用mysqli

$mysqli = new mysqli("localhost", "username", "password", "database");
if ($mysqli->connect_errno) {
    echo "Failed to connect to MySQL: " . $mysqli->connect_error;
    exit();
}

$stmt = $mysqli->prepare("SELECT * FROM wp_users WHERE user_id=?");
$stmt->bind_param("i", $user_id);
$user_id = $_GET['user_id']; // 假设这是用户输入
$stmt->execute();
$result = $stmt->get_result();

<?php
/*
Plugin Name: My Custom Database Plugin
*/

function my_custom_db_query() {
    global $wpdb;

    // 使用 $wpdb 对象进行查询，这是 WordPress 提供的数据库抽象层
    $results = $wpdb->get_results("SELECT * FROM {$wpdb->prefix}posts WHERE post_type='post'");

    foreach ($results as $post) {
        echo "Post ID: " . $post->ID . "<br>";
        echo "Title: " . $post->post_title . "<br>";
        echo "Content: " . $post->post_content . "<br><br>";
    }
}

add_action('admin_menu', 'my_custom_db_menu');

function my_custom_db_menu() {
    add_menu_page('My Custom DB Page', 'My DB Plugin', 'manage_options', 'my-custom-db-plugin', 'my_custom_db_query');
}